Department of Microbiology, University of Kalyani, Kalyani, West Bengal, 741235, India.
Environ Geochem Health. 2019 Oct;41(5):1953-1966. doi: 10.1007/s10653-019-00261-2. Epub 2019 Feb 14.
Comprehensive studies on the effect of arsenic (As) on free-living diazotrophs that play a crucial role in soil fertility by nitrogen fixation are still scanty. Here, we isolated three free-living bacteria from rice field with potential nitrogen-fixing ability and investigated the impact of As on their nifH gene expression and extracellular polysaccharide (EPS) production in culture condition and soil system. 16S rRNA sequence analysis showed that the isolated bacteria were affiliated to β-Proteobacteria, γ-Proteobacteria and Firmicutes. As(III) exposure to bacterial isolates followed by RT-qPCR analysis revealed that elevated levels of As reduced the expression of nifH gene in selective bacteria, both in culture medium and soil condition. We also noticed reduced production of EPS under higher concentration of As. All the three bacteria showed high tolerance to As(III), able to oxidize As and exhibited significant plant growth-promoting traits. This investigation indicated that an environment exposed with higher concentration of As might perturbed the activity of free-living diazotrophs in agricultural soil system.
综合研究砷（As）对在土壤肥力中起着关键作用的自由生活固氮菌的影响仍然很少。在这里，我们从稻田中分离出了具有固氮潜力的三种自由生活细菌，并在培养条件和土壤系统中研究了砷对其 nifH 基因表达和胞外多糖（EPS）产生的影响。16S rRNA 序列分析表明，分离出的细菌属于β-变形菌、γ-变形菌和厚壁菌门。用 As(III) 处理细菌分离物，然后进行 RT-qPCR 分析表明，在培养介质和土壤条件下，较高水平的 As 降低了选择细菌中 nifH 基因的表达。我们还注意到在较高浓度的 As 下 EPS 的产生减少。所有三种细菌对 As(III) 都表现出很高的耐受性，能够氧化 As，并表现出显著的植物生长促进特性。这项研究表明，暴露在较高浓度 As 环境中的土壤可能会扰乱农业土壤系统中自由生活固氮菌的活性。
